Open heart surgery, such as a triple bypass or aortic artery repair, often requires stopping the patient's heart. A cardiopulmonary bypass machine (“heart-lung machine”) comprising a pump and a membrane oxygenator is used to assist or replace normal heart function by circulating and oxygenating the patient's blood during the operation.
Heart-lung machines provide only very short-term (3-5 hours) cardiac function during surgery. However, many end-stage chronic heart failure patients require intermediate, long-term and even permanent cardiac assistance. For example, an artificial heart pump may be used to keep a patient alive while he is waiting for a donor organ to become available. Other patients may require cardiac assistance after cardiac surgery. The domestic demand for a simple, long-term ventricle assist device has been estimated at between 50,000 and 100,000 patients/year.
One of the first artificial ventricles was a pneumatically driven left ventricle, implanted in a patient in 1967. An air pump was located outside the patient's body, and a hose extended from the air pump to the implanted device.
There has been a demand ever since for a ventricular assist device which is completely implantable (without any protruding drive, vent or control cables), produces a pulsatile perfusion pattern, has a reliable long term power supply and a long service life, and is quiet. Unfortunately, known devices which seek to mimic native heart function suffer from high energy requirements, which in turn require external (extracorporeal) power sources.
The need for an extracorporeal power source requires an electrical cable to break the skin, which poses an increased risk of serious infection and, not incidentally, can be painful.
The high energy requirement of known devices means they have a short service life. Thus, patients must either change battery packs every few hours or remain within a short distance from a power outlet. The patient's mobility and quality of life are seriously comprised.
Piezoelectric motors which have relatively low power requirements, little heat dissipation and little noise generation have been suggested for heart assist devices. However, piezoelectric drive systems have also been unsuccessful because their output frequency, pressure and displacement are incompatible with those of the human heart.
In short, there is a long-felt but heretofore unsatisfied need for a totally implantable device which can provide long term cardiac assistance (pulsatile perfusion) without drastically reducing the patient's quality of life.